large volume of air into the altitude chamber.When you open the chamber bleed valve (K),ambient air flows into the chamber through thechamber bleed port (CB). The altitude in thechamber drops until the pressure inside thechamber equalizes with the pressure at sea level.PRESSURIZING THE CHAMBERBLEED SYSTEMOpen the vacuum control valve (B1) andascend to 10,000 feet; then close the valve tostabilize your altitude. A drop in altitude on thelow-range altimeter (13) indicates a leak. If thereis no drop in altitude, open the chamber bleedvalve (K) and descend to sea level. When youreach sea level, close the chamber bleed valve (K).The test stand is now ready to test the flowmeasuring system.FLOW MEASURING SYSTEMThis system is the largest and most importantsystem on the test stand. The purpose of the flowmeasuring system is to measure flows of air,nitrogen, or air/nitrogen mixture from an itemunder test. As you can see in figure 2-11, thesystem consists of vol-o-flow elements, flowindicating manometers, control valves, and selec-tor valves. The flow measuring system is madeup of the output, input, and vent flow subsystems.The different subsystems function with thevacuum running.OutputThe output flow system originates at thepiezometer (26) and flows through the outputport (23) to the flow selector valve (M). Itis then directed to either the output vol-o-flowe l e m e n t o r t h e s u i t s i m u l a t o r t a n k . W h enthe flow selector valve (M) is placed in theREGULATOR position, the flow is directedto the output vol-o-flow element. The volumeof flow is controlled by the output valve (C) andis indicated on the output flow manometer (l).The only time this system is used with the flowselector valve (M) in the SUIT SIMULATORposition is when the full pressure suit breathingregulator is tested.Figure 2-11.Model 1172AS100 flow measuring system.2-12